[clang] Look through parens around reinterpret_cast to emit a warning #157033
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Clang warns about UB when a reinterpret_cast is dereferenced as an incompatible type: long l; *reinterpret_cast<double*>(&l) // UB However, the code was too strict and did not handle extra parens around a reinterpret_cast, so the following case was not diagnosed: long l; *(reinterpret_cast<double*>(&l)) // UB, but no warning The patch now skips ParenExpr when looking for a CXXReinterpretCastExpr to enable a diagnostic for the second case.
llvmbot
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@llvm/pr-subscribers-clang Author: Andrew Savonichev (asavonic) ChangesClang warns about UB when a However, the code was too strict and did not handle extra parens around a The patch now skips ParenExpr when looking for a CXXReinterpretCastExpr to enable a diagnostic for the second case. Full diff: https://github.com/llvm/llvm-project/pull/157033.diff 2 Files Affected:
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 8565b18078185..f7e02805ae9d0 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -14774,7 +14774,7 @@ static QualType CheckIndirectionOperand(Sema &S, Expr *Op, ExprValueKind &VK,
QualType OpTy = Op->getType();
QualType Result;
- if (isa<CXXReinterpretCastExpr>(Op)) {
+ if (isa<CXXReinterpretCastExpr>(Op->IgnoreParens())) {
QualType OpOrigType = Op->IgnoreParenCasts()->getType();
S.CheckCompatibleReinterpretCast(OpOrigType, OpTy, /*IsDereference*/true,
Op->getSourceRange());
diff --git a/clang/test/SemaCXX/reinterpret-cast.cpp b/clang/test/SemaCXX/reinterpret-cast.cpp
index bfb808773b900..fdaa17a35eb8b 100644
--- a/clang/test/SemaCXX/reinterpret-cast.cpp
+++ b/clang/test/SemaCXX/reinterpret-cast.cpp
@@ -167,6 +167,9 @@ void dereference_reinterpret_cast() {
(void)reinterpret_cast<float&>(d); // expected-warning {{reinterpret_cast from 'double' to 'float &' has undefined behavior}}
(void)*reinterpret_cast<float*>(&d); // expected-warning {{dereference of type 'float *' that was reinterpret_cast from type 'double *' has undefined behavior}}
+ // Look through parens
+ (void)*(reinterpret_cast<double*>(&l)); // expected-warning {{dereference of type 'double *' that was reinterpret_cast from type 'long *' has undefined behavior}}
+
// TODO: add warning for tag types
(void)reinterpret_cast<A&>(b);
(void)*reinterpret_cast<A*>(&b);
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Fznamznon
reviewed
Sep 5, 2025
shafik
reviewed
Sep 6, 2025
| @@ -167,6 +167,9 @@ void dereference_reinterpret_cast() { | |||
| (void)reinterpret_cast<float&>(d); // expected-warning {{reinterpret_cast from 'double' to 'float &' has undefined behavior}} | |||
| (void)*reinterpret_cast<float*>(&d); // expected-warning {{dereference of type 'float *' that was reinterpret_cast from type 'double *' has undefined behavior}} | |||
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| // Look through parens | |||
| (void)*(reinterpret_cast<double*>(&l)); // expected-warning {{dereference of type 'double *' that was reinterpret_cast from type 'long *' has undefined behavior}} | |||
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I am assuming this ignores multiple parens, maybe worth a test?
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Sure, added a test.
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Thanks! Done. |
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Clang warns about UB when a
reinterpret_castis dereferenced as an incompatible type:However, the code was too strict and did not handle extra parens around a
reinterpret_cast, so the following case was not diagnosed:The patch now skips ParenExpr when looking for a CXXReinterpretCastExpr to enable a diagnostic for the second case.